What's the operating system of your PC, Windows 7? Try to enable WLAN Autoconfig and try again. http://www.tp-link.com/en/faq-306.html If it doesn't work, uninstall the driver, uninstall anti-virus...

Did you use POE injector in the package? How did you connect? PoE port on the injector is connected to LAN port of WA901ND and LAN port on the injector is connected to your router or switch?

Try to upgrade the latest firmware for WR841N V9. http://www.tp-link.com/en/download/TL-WR841N_V9.html#Firmware

Archer C5 or any other model? V2 is the newer than V1.2 and there are some hardware changes. V2 should work better in Wi-Fi performance.

1. Is the drive compatible with D9? http://www.tp-link.com/en/faq-603.html 2. How to access to the driver? http://www.tp-link.com/en/faq-648.html

Can you describe in details?